Project Summary/Abstract UNAIDS estimates the global population of children under 15 years of age HIV-exposed yet uninfected (CHEU) approached 15 million in 2018, and each year more than 1 million newborns continue to be HIV-exposed uninfected, the overwhelming majority of whom reside in low- and middle-income countries. Evolving public health responses have contributed to the heterogeneity of in utero exposures for CHEU. As the HIV epidemic has matured, pregnant women living with HIV (WLHIV) are accessing more potent antiretroviral regimens prior to and during pregnancy. While this has dramatically reduced infant HIV acquisition, safety monitoring of antiretroviral treatment (ART) in pregnancy has been limited. Even with exposure heterogeneity, both children and youth HEU continue to experience higher risk for poorer outcomes compared with children HIV-unexposed and uninfected (CHUU). Our work and the work of others has shown increased risk of infectious morbidity, mortality, poorer growth, altered metabolic health, and neurobehavioral delays and deficits. It is imperative that modifiable biological, social, and structural mechanisms driving these disparities be identified to inform interventions. Botswana has the 2nd highest prevalence of HIV worldwide. Yet, it was the first country in sub- Saharan Africa to provide free ART to its citizens including pregnant women, leading the continent in the response to the HIV epidemic and in adoption of new ARVs, including dolutegravir. Concurrently, Botswana ? Harvard AIDS Institute Partnership (BHP) has been conducting cutting-edge research involving pregnant WLHIV and their children since 2001 when the Mashi study (R01HD37793) opened. We have captured uniform and harmonized data, including obstetric and maternal ART information, infant birth data, infant antiretroviral (ARV) prophylaxis type and duration, infant duration of breast and/or formula feeding and other socioeconomic data. Our curated database contains information on >5,000 CHEU. Leveraging our robust database, we will establish the FLOURISH cohort (Following Longitudinal Outcomes to Understand, Report, Intervene, and Sustain Health of Infants, Children and Adolescents who are HIV-Exposed Uninfected) of 1,575 child/adolescent-caregiver pairs (1100 CHEU, 475 CHUU). The FLOURISH cohort will enable us to evaluate differences in rates of infectious morbidity and all-cause mortality between CHEU and CHUU up to 3 years of age. Among school-aged children (6-10 years of age), we will assess whether in utero HIV/ARV exposure among CHEU is associated with differences in neurobehavioral functioning compared with CHUU. Lastly, among children ? 10 years of age, we will assess associations between in utero HIV/ARV exposure and cardiometabolic risk factors using age, sex, and body mass index (BMI)-frequency matched CHUU as a comparator. The rich breadth of well-characterized seminal BHP studies will provide a robust platform from which key scientific questions regarding life course outcomes of CHEU can be answered, informing the design of interventional trials and mechanistic studies.